I have been looking at a tutorial from DappUniversity about Web3... on the introductory video, I have completed all stages fine, but when getting to retriving account balance information from the mainnet ( i picked a random account from the Etherscan.io) it doesn't retrieve it.

I get an error like this when looking at the balance on its own ---|> web3.eth.getBalance(address, (err, bal) => { balance = bal })
the respond is 'undefined' and does not return a account value in Wei...

I tried getting to read the balance error through --|> web3.eth.getBalance(address)

With regards to the error UnhandledPromiseRejectionWarning: Error: Invalid JSON RPC response: "" Does it occur while calling getBalance()? It might be helpful to post a more detailed code also to better help resolve this error.